This invention relates to a fuel supply control apparatus for an internal combustion engine and, more particularly, to an air fuel ratio control apparatus suitable for use with an automobile gasoline engine.
As a system for supplying fuel to the combustion chambers of a gasoline engine, a fuel supply system using a carburetor has heretofore been employed. This system which employs a carburetor utilizes a negative pressure of suction of the engine. It is therefore difficult to perform control to obtain an accurate air fuel ratio (A/F) for all the operational conditions of the engine. For this reason, there has been widely utilized a fuel supply system in which the fuel is fed into the combustion chamber of the engine by injecting fuel through a suction pipe with the aid of a fuel injection valve which is electronically controlled.
An example of such an electronic engine control system is disclosed in U.S. Pat. No. 4,363,097. The system comprises a microcomputer, a peripheral control circuit which is connected to receive various data, such as air flow rate, temperature of engine cooling water, air fuel ratio, r.p.m. of the engine, etc. Control signals obtained on the basis of this data are supplied to a fuel injection pump, a bypass valve, exhaust gas recirculation (EGR) control valve, and a fuel to effect fuel supply amount control by controlling the fuel injection valve, idling r.p.m. control by controlling the bypass valve, and control EGR by controlling the EGR valve.
There is also provided a throttle sensor mounted on a throttle valve for detecting throttle valve opening. The opening data for the throttle valve obtained through the sensor is fetched by the microcomputer.
The control system calculates, by use of the microcomputer, fuel supply amount per unit time, based on the data of the air fuel ratio and the r.p.m. of the engine. The fuel injection value is constructed so as to provide a fixed in fuel amount per unit time, so that the injection fuel amount being supplied to the cylinder is a function of fuel injection time. Therefore, the fuel injection amount is determined by the fuel injection time, with compensation being made therefor by various factors.
Among the various kinds of compensation required for controlling the engine, a conventional electronic fuel injection system provides a so-called fuel increase compensation during acceleration and fuel decrease compensation during deceleration. Such compensation is effective according to operational conditions of the throttle valve. Namely, when the throttle valve is operated for acceleration, the fuel injection amount is compensated to be excessively rich, while it is compensated to be excessively lean when the throttle valve is operated for deceleration, whereby a desired engine performance can be achieved. However, such an engine control system employing conventional fuel compensation for acceleration and deceleration has a defect in that an abrupt change in engine torque is apt to occur during acceleration and such a torque change detracts from the type of comfortable smooth ride desired from the automobile.